1. Field of the Invention
The present invention relates generally to a method and apparatus for wavelength conversion.
2. Description of Related Art and General Background
In an all-optical network, if two optical packets, each carried within the same wavelength range but on two different optical fibers, arrive simultaneously at an input of the optical switch, a wavelength conversion device may be used to change the wavelength of one of the packets so that both packets can be passed to a single output fiber without loss of either packet. Simultaneous arrival of packets can result in packet blocking and/or information loss, which can require a packet to be transmitted multiple times, thereby reducing the actual performance of a network much below the theoretical performance. In order to reduce the probability of packet blocking, it may be desirable to employ a wavelength conversion device. A wavelength conversion device can convert an optical signal from a first wavelength to a second wavelength within the optical network, thereby reducing problems with contention resolution.
Wavelength conversion may be all-optical, or it may make use of an optical receiver which provides an electrical signal to a tunable laser transmitter. All-optical wavelength conversion generally makes use of semiconductor optical amplifiers such as are disclosed in U.S. Pat. No. 6,069,732 to Koch et al.
Conventional wavelength conversion systems make use of out of band wavelength conversion, where “band” refers to, for example, a conventional International Telecommunication Union (ITU) window as used in dense wavelength division multiplexing (DWDM). (See, for example, ITU-T Recommendation G.692, Optical interfaces for multichannel systems with optical amplifiers, 10/1998). Such a window is generally between about 0.2 and 0.4 nm wide. Thus, in conventional wavelength conversion, in a DWDM system which encompasses several ITU windows from λ1 to λ4, a wavelength λ1 will be converted to λ5 or λ6 (i.e. outside of the range λ1 to λ4) in order to resolve contention problems. This out of band conversion can result in difficulty with tracking converted packets. Moreover, if λ5 is somewhat distant from λ1, there will generally be a problem caused by low conversion efficiency.